Five Fun Facts about NREL’s New Solar Windows Innovation

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Thanks to Energy Department funded research and development (R&D), a group of National Renewable Energy Laboratory (NREL) scientists recently made a significant breakthrough in solar windows. The NREL scientists created solar windows that use thermochromism—the property of substances to change color due to a change in temperature—to transform from transparent to tinted, and convert sunlight into electricity in that tinted state.

The innovation, called SwitchGlaze, could be one of the next commercial successes coming from Energy Department national laboratory research. The SwitchGlaze team has been able to explore the market potential of their new technology through Technology-to-Market’s Energy I-Corps, a training program for national lab researchers that aims to accelerate industry offtake of DOE technologies. With support from the Building Technologies Office (BTO), the researchers spent two months learning the industry landscape for solar windows, and determining how to best transition their technology from the lab to the marketplace.

While this technology offers something new and exciting to the market, solar windows have been around for decades. Initial efforts integrated conventional fully-opaque solar cells into windows and shades. This was followed by semi-transparent designs when thin film solar technology took hold. The latest technologies included fully-transparent, infrared light-absorbing designs.

What makes their technology unique? Read below for five fun facts about solar windows and how this new innovation works, with help from Dr. Lance Wheeler, NREL researcher and Principal Investigator of SwitchGlaze.

1. It looks like an ordinary window. SwitchGlaze windows may look ordinary, but they are far from it. The technology absorbs some of the sunlight as it is transmitted through the window and converts it into electricity. The windows act like solar cells, providing a flexible clean energy solution for modern building design.

2. It “switches” with changes in temperature. SwitchGlaze solar windows are designed to tint (the switch) at warmer temperatures, especially on hot days when the sun is shining. After the switch to a tinted state occurs, SwitchGlaze windows absorb and convert sunlight into electricity the same way conventional rooftop solar panels do. A switchable solar window has the potential for higher efficiency because it switches to be darker (more absorbing) than static window photovoltaics.

3. It’s thermochromic. SwitchGlaze windows use temperature-triggered thermochromic tinting. This is what allows for the partial absorption of sunlight and transforms the windows into efficient solar cells. SwitchGlaze initially converts sunlight into electricity at an efficiency of 11.3%. Conventional rooftop solar panels are roughly 20% efficient, with a theoretical maximum of 32%. Meanwhile solar windows that only convert non-visible (infrared and ultraviolet) light are limited by a theoretical 20% efficiency.

4. It will be cost efficient. The cost of adding SwitchGlaze solar cell layers to traditional windows is predicted to be a fraction of the cost, which could be cancelled out by solar energy payback. The most expensive parts of conventional rooftop solar panels, the glass that encapsulates the panel and the transparent metals, are already in standard high-performance windows. In addition, because of their ability to tint, SwitchGlaze windows may save on building cooling costs in the summer.

5. It’s an evolving technology. Building design is constantly evolving from static to dynamic. Just like lighting set to motion sensors provides lighting when needed by responding to occupant need, this dynamic technology responds to sunlight to improve building efficiency and provide on-site energy generation. Buildings of the future will be more energy-efficient, comfortable, and durable as dynamic technologies are integrated. SwitchGlaze is currently in the proof-of-concept stage, with more work to be done before it will be commercially available.

Erik Hyrkas is originally from the Twin Cities and completed his undergraduate at Lakeland College of Sheboygan, Wisconsin. He has been working with the Energy Department's EERE Communications in Washington, D.C. since February 2010. Erik is also longtime freelance writer and technology fanatic who loves to play tennis, swim, and draft an occasional blog.